Drop-on-demand ink jet printers use thermal energy to produce a vapor bubble in an ink-filled chamber to expel a droplet. A thermal energy generator or heating element, usually a resistor, is located in the chamber on a heater chip near a discharge orifice. A plurality of chambers, each provided with a single heating element, are provided in the printer's printhead. The printhead typically comprises the heater chip and a nozzle plate having a plurality of the discharge orifices formed therein. The printhead forms part of an ink jet print cartridge, which also comprises an ink-filled container.
The resistors are individually addressed with an energy pulse to momentarily vaporize the ink and form a bubble that expels an ink droplet. A flexible circuit is used to provide a path for energy pulses to travel from a printer energy supply circuit to the printhead. The flexible circuit includes a substrate portion and a plurality of traces located on the substrate portion. The traces have end sections that extend out from the substrate portion. The extending sections are coupled to bond pads on the printhead. Typically, there is a first row of coupled bond pads and trace sections and an opposing, second row of coupled bond pads and trace sections.
It is known in the art to form a barrier layer over each row of coupled bond pads and extending trace sections. One known process for forming such a barrier layer involves dispensing an encapsulant material onto the coupled bond pads and trace sections using a discharge needle. The final height of the barrier layer relative to the nozzle plate typically is undesirably high. As a result, a paper substrate, which receives the ejected ink droplets, is spaced an increased distance from the printhead orifice plate. Consequently, misdirected ink droplets reach the paper substrate at locations which are spaced a greater distance from their intended contact points than if the paper substrate were located closer to the printhead orifice plate. The excessive height of the barrier layer is further problematic as it makes it more difficult to apply a length of sealing tape to the printhead so as to seal the printhead orifices from ink leakage until the print cartridge is installed for use in a printer. Another potential problem associated with dispensing an encapsulant material with a discharge needle relates to improper location. Dispensing encapsulant in the wrong locations can result in unacceptable product because the encapsulant fails to provide the necessary coverage for the electrical components on the print cartridge.
One method for providing encapsulant on an inkjet printhead that addresses some of the problems associated with needle dispensing utilizes stencil printing to apply the encapsulant. Commonly assigned U.S. patent application Ser. No. 10/679,070 describes a method of stencil printing an encapsulant material over electrical connections and other areas on an inkjet printhead. Typical stencil printing operations are considered discontinuous in that a single stencil is used to apply encapsulant to a number of components. The component to be stencil printed is positioned in the stencil printer under a stencil, the stencil and part to be printed are brought into contact and an encapsulant is deposited on the stencil and squeezed through the holes of the stencil by a squeegee which is moved across the upper face of the stencil. When the printing is complete, the stencil is lifted off the substrate and the substrate is removed so that the process can be repeated with additional substrates. Because this process is discontinuous, it is slow, time consuming and, therefore, relatively expensive.
The conventional stencil printing process can also involve a build up of excess encapsulant in or around the holes of the stencil, that can impede flow of the encapsulant to the substrate. Furthermore, encapsulant may also build up on the underside of the stencil adjacent to the holes. In either case, the build up of excess adhesive on the stencil can lead to poor quality printheads. As the requirement for inkjet printhead print quality increases, the need for a clean stencil surface also increases so that the inkjet printhead nozzles are kept free of excess encapsulant. Options available for keeping the stencil clean are limited. Operators may resort to manually wiping the excess encapsulant from the stencil. However, this may not be sufficient to dislodge encapsulant gathered in the holes of the stencil. Furthermore, manual removal of excessive encapsulant is labor and time intensive and not always reliable. In a conventional stencil printing process, the buildup of material on the underside of the stencil requires a separate wiping process. This underside wiping step increases the process cycle time and effectively makes the conventional stencil printing process discontinuous.
Therefore, it would be desirable to provide a method of cleaning excessive encapsulant from the stencil that can be included as part of a continuous operation. Furthermore, it would be desirable to provide a stencil printing method capable of applying encapsulant to a variety of printhead designs as part of a continuous printing operation.